Consumption vs. deposition of essential fatty acids in gilthead sea bream (Sparus aurata) larvae fed semi-purified diets

Semi-purified diets were used to feed gilthead sea bream larvae as first food from mouth opening until day 17. Four diets were formulated on the basis of a previous one used as control (D1). Three experimental diets differed only by the lipids added. One diet contained n-3 highly unsaturated fatty acids (n-3 HUFA) plus arachidonic acid (D2), one diet n-3 HUFA without arachidonic acid (D3) and one diet without n-3 and n-6 HUFA (D4). The three experimental diets contained 18:3n-6 in order to follow the influence of dietary HUFAs on elongation-desaturation capacities. Larval growth and survival were similar with diet D1 and D2. Lowest growth and survival were observed for larvae fed the HUFA free diet D4. Larval survival but not growth was significantly decreased by lack of arachidonic acid in diet D3 compared to D2. Utilization of fatty acids by larvae was studied by comparing the fatty acid quantities per larva in initial (before feeding) and final samples. In larvae fed the HUFA-free diet D4, a significant increase of 20:3n-6 showed that some elongation from 18:3n-6 occurred, while quantities of arachidonic acid and n-3 fatty acids (except 18:3n-3) decreased compared to initial larvae. A consumption of endogenous HUFAs was evidenced despite effective incorporation of dietary fatty acids such as 18:2n-6, 18:1n-9 and 18:3n-3. Fatty acid profile of these larvae changed, according to dietary fatty acid influence, by turnover rather than by a raw incorporation of fatty acids. Larvae fed the n-3 HUFA diet depleted in arachidonic acid (D3) had a total fatty acid content lower than those fed with arachidonic acid (D2); compared to those fed D4, the elongation of 18:3n-6, to 20:3n-6 seemed to be repressed by dietary n-3 HUFA. Consumption of long-chain unsaturated fatty acid is a main conclusion of this study; a rate of loss around 1.1, 0.5 and 0.05 mg day(-1) g(-1) mean dry body weight of larvae for docoshexaenoic, eicosapentaenoic and arachidonic acid, respectively, may be estimated in larvae fed the HUFA free diet D4. No desaturation capacities of gilthead sea bream larvae were evidenced; however, some low capacities might be masked by the consumption of HUFAs.